Neurofibromatosis (NF) consists of two or more distinct autosomal dominant genetic disorders characterized by abnormalities of cells derived from the neural crest and is associated with the development of several types of nervous system tumors. Recently the NF1 gene was isolated and shown to share homology with GTPase-activating (GAP) proteins. The long-term objective of this project is to determine the roles of the NF1 and NF2 genes in the formation of tumors in NF. The first goal will be to determine the clonal origin of nervous system tumors using molecular genetic techniques and thus gain useful insights into the neoplastic process. Tumors to be analyzed include neurofibromas, neurofibrosarcomas, gliomas and other glial tumors associated with NF. The clonal origin of melanocytes cultured from cafe-au-lait spots will also be determined. Clonal analysis will be performed using DNA polymorphisms in the X chromosome genes hypoxanthine phosphoribosyltransferase (HPRT) or phosphoglycerate kinase (PGK). The results will be correlated with loss of genetic material in the same tumors. If a tumor has a clonal origin, it implies that a single mutation was the primary event. If a tumor is multicellular in origin, it suggests modulation by an environmental factor, such as a carcinogen or infectious agent. The second goal will be to determine the levels of NF1 gene expression in neural crest-derived cells and tumors. NF1 messenger RNA will be analyzed by Northern blot hybridization, S1 nuclease protection assays, PCR amplification, and by in situ hybridization. Tissues to be examined include normal Schwann cells, Schwann cell and astrocytic tumors, and also normal melanocytes and melanocytes from cafe-au-lait spots. These investigations should reveal quantitative or qualitative alterations in the NF1 messenger RNA. These studies should increase our understanding of the mechanisms by which tumors arise in NF and should facilitate their treatment.